Talk Blogging

Hey everyone, I'm wanting to start a blog (huh, me and half the western world, did I hear you say :-), but I need some help finding the right software/host/Thingy for my needs.

Some ideas about the sort of things I'll need it to do:

1) blog will be about a specific topic--eg, 'Developments in brain surgery', or 'the quest for the right shade of lipstick' :-)--rather than a more general journal of what's going on in my life. Therefore, the people I'd be writing for would be just about anyone sharing an interest in said topic, rather than family and friends visiting the blog to keep in touch. Hence, I think it might be best if the software/host etc is pretty visible, as we're looking at people coming through via various links rather than being given a specific address to visit, by myself, in person.
2) I think I'd prefer something where I don't need to pay/commit to a length of time, or download anything--in case I don't take to blogging after all, makes it easier to dump the project.
Oh, forgot to add: I already know about the blogs as part of MySpace and Facebook, etc, which are a nice idea but I was looking for something independent of social networking stuff (remember that bit about it not being specifically for friends and family...). I know about blogger as well (I'd have to have been living under a rock not to :-) and I've also seen wordpress.com, which I rather like the look of. but I was wondering if there are any other interesting possibilities than these, which I may just not have heard of *shrug*

One last thing: I'll be mainly blogging from a Mac, and thought I'd add this in case there are some things that work better with one platform rather than another (don't start screaming if it's stupid lol, I don't know enough about blogging software to be able to tell if it's irrelevant :-))

Thanks !